1. Field of the Disclosed Subject Matter
The presently disclosed subject matter is related to the delivery of therapeutic agents from an interventional medical device. More particularly, the presently disclosed subject matter relates to an interventional device for delivery of therapeutic agents from an expandable member, such as a balloon. The disclosed subject matter also relates to a method and apparatus for maintaining a fixed distance between a dispenser and the balloon surface during application of one or more therapeutic agents onto the expandable member as well as the assembly of the medical device.
2. Description of Related Subject Matter
Atherosclerosis is a syndrome affecting arterial blood vessels. It is characterized by a chronic inflammatory response in the walls of arteries, which is in large part due to the accumulation of lipid, macrophages, foam cells and the formation of plaque in the arterial wall. Atherosclerosis is commonly referred to as hardening of the arteries, although the pathophysiology of the disease manifests itself with several different types lesions ranging from fibrotic to lipid laden to calcific. Angioplasty is a vascular interventional technique involving mechanically widening an obstructed blood vessel, typically caused by atherosclerosis.
During angioplasty, a catheter having a folded balloon is inserted into the vasculature of the patient and is passed to the narrowed location of the blood vessel at which point the balloon is inflated to the desired size by fluid pressure. Percutaneous coronary intervention (PCI), commonly known as coronary angioplasty, is a therapeutic procedure to treat the stenotic regions in the coronary arteries of the heart, often found in coronary heart disease. In contrast, peripheral angioplasty, commonly known as percutaneous transluminal angioplasty (PTA), generally refers to the use of mechanical widening of blood vessels other than the coronary arteries. PTA is most commonly used to treat narrowing of the leg arteries, especially, the iliac, external iliac, superficial femoral and popliteal arteries. PTA can also treat narrowing of carotid and renal arteries, veins, and other blood vessels.
Although the blood vessel is often successfully widened by angioplasty, sometimes the treated region of the blood vessel undergoes vasospasm, or abrupt closure after balloon inflation or dilatation, causing the blood vessel to collapse after the balloon is deflated or shortly thereafter. One solution to such collapse is stenting the blood vessel to prevent collapse. Dissection, or perforation, of the blood vessel is another complication of angioplasty that can be improved by stenting. A stent is a device, typically a metal tube or scaffold that is inserted into the blood vessel after, or concurrently with angioplasty, to hold the blood vessel open.
While the advent of stents eliminated many of the complications of abrupt vessel closure after angioplasty procedures, within about six months of stenting a re-narrowing of the blood vessel can form, a condition known as restenosis. Restenosis was discovered to be a response to the injury of the angioplasty procedure and is characterized by a growth of smooth muscle cells and extracellular matrix—analogous to a scar forming over an injury. To address this condition, drug eluting stents were developed to reduce the reoccurrence of blood vessel narrowing after stent implantation. A drug eluting stent is a stent that has been coated with a drug, often in a polymeric carrier, that is known to interfere with the process of re-narrowing of the blood vessel (restenosis). Examples of various known drug eluting stents are disclosed in U.S. Pat. Nos. 5,649,977; 5,464,650; 5,591,227, 7,378,105; 7,445,792; 7,335,227, each of which are hereby incorporated by reference in their entirety. However, a drawback of drug eluting stents is a condition known as late stent thrombosis. This is an event where a blood clot forms inside the stent, which can occlude blood flow.
Drug coated balloons are believed to be a viable alternative to drug eluting stents in the treatment of atherosclerotic lesions. In a study which evaluated restenosis, and the rate of major adverse cardiac events such as heart attack, bypass, repeat stenosis, or death in patients treated with drug coated balloons and drug eluting stents, the patients treated with drug coated balloons experienced only 3.7 percent restenosis and 4.8% MACE (major adverse coronary events) as compared to patients treated with drug eluting stents, in which restenosis was 20.8 percent and 22.0 percent MACE rate. (See, PEPCAD II study, Rotenburg, Germany)
However, drug coated balloons present certain unique challenges. For example, the drug carried by the balloon needs to remain on the balloon during delivery to the lesion site, and released from the balloon surface to the blood vessel wall when the balloon is expanded inside the blood vessel. For coronary procedures, the balloon is typically inflated for less than one minute, typically about thirty seconds. The balloon inflation time may be longer for a peripheral procedure, however typically even for peripheral procedures the balloon is expanded for less than 5 minutes. Due to the short duration of contact between the drug coated balloon surface and the blood vessel wall, the balloon coating must exhibit efficient therapeutic agent transfer and/or efficient drug release during inflation. Thus, there are challenges specific to drug delivery via a drug coated or drug eluting balloon that are not present with a drug eluting stent.
Furthermore, conventional techniques for applying a coating, such as a therapeutic agent, may not be desirable for coating balloons, or other expandable members of medical devices. Such convention techniques include spraying (air-atomization, ultrasonic, electrostatic, etc.), dip-coating, spin-coating, vapor deposition, roll coating, micro-droplet coating, etc. Balloons present a cylindrical surface to be coated where it is desired to uniformly coat only the working length of the balloon and no other portion of the balloon or catheter. Techniques such as spraying are needed to coat the fine geometry of stents without webbing but are very inefficient, with a low coating efficiency. However, balloons do not have this requirement and the low drug utilization efficiency is undesirable, particularly for large peripheral balloons. Many of these conventional techniques do not provide sufficient coating uniformity or edge control. For example, it is often desirable to apply the coating to balloon surface when the balloon is at least partially inflated, however balloons which are not cylindrical in shape when expanded, such as peripheral balloons, often warp or bow upon inflation. Consequently, a non-uniform coating is applied to the balloon surface thereby leading to a non-uniform drug distribution with even the potential for bare spot with no coating. In addition, this compromises the efficiency in the coating process, can degrade the efficacy of the therapeutic agent, and an inappropriate coating process can lead to further distorting or bowing of the balloon.
Thus there remains a need, and an aim of the disclosed subject matter is directed towards, maintaining a fixed distance between the coating dispenser and the surface of the balloon during the application of one or more therapeutic agents to the surface of an expandable member of a medical device.